This invention relates to a "large-scale testing apparatus for water vapor resistance (permeance) determination" of vapor barriers, used in thermal insulation of building envelope systems (e.g. curtain walls, metal buildings, brick and mortar structures, etc.) and in mechanical insulation systems and air handling products (e.g. pipings, ducts and equipment, etc.), in conditions which approximate the service situation. They do provide values that permit the proper vapor barrier design under different conditions of temperature and relative humidity found in service.
The method consists of testing large-scale vapor barrier specimens, installed either on a rigid support plate with known hygro-thermal properties, of different materials (e.g. reinforced concrete, ply board, insulation, etc.), in building envelope systems or directly on the thermal insulation with real thickness in mechanical insulation systems, in function of the vapor barrier type: membrane or mastic and coating and of the using field by means of a "large-scale cold cup," applied on the cold side of the specimen assembly. This cup performs the effect of a "cold surface" upon which vapor condensation occurs.
The water originated of condensation represents the vapor quantity, which passes through the vapor barrier-support assembly.
The specimen and cold cup assembly is positioned tightly between two controlled temperature and relative humidity "warm" and "cold chambers" which conditions approach to the service conditions. All the research and testing institutes are equipped with such controlled atmosphere chambers or with the installations able to realize a controlled atmosphere in special spaces. This method gives the opportunity to test the vapor barriers resistance (permeance) in different interior and exterior service conditions. In this case, the testing values can be considered as "design data."
The conventional vapor permeability test consists of two basic methods: the "dry cup" or "dessicant method" and the "wet cup" or "water method," applied on small-scale specimens. Both methods provide "isothermal conditions" for materials testing. In the "dry cup" or "dessicant method," the relative humidity inside is approximately 0%. In the "wet cup" or "water method," the relative humidity inside is approximately 100%. The dry or wet cups are placed into a controlled test chamber (room or cabinet), with constant temperature and relative humidity. The temperature is between 70.degree. and 90.degree. F. (21.degree. and 32.degree. C.) and shall be maintained constant +1.degree. F. (0.6.degree. C.). The relative humidity is maintained at 50+2%, except where extreme of humidity and temperature are desired: 100+1.degree. F. (38+0.6.degree. C.) temperature and 90+2% relative humidity. In these circumstances, the vapor barrier resistances obtained by the conventional methods represent very high values, for example of 150. . . 200 m..sup.2 h.mmHg/g for bituminous, rubber, or plastic coatings, of 300. . . 550 m..sup.2 h.mmHg/g for plastic membranes, of 500. . . 2000 m..sup.2 h.mmHg/g for bituminous multilayer roofings and in the case of metal membranes much more higher than these values. These values are much higher than these obtained by the large-scale cold cup method. The explanation is that the conventional methods consider only a few service factors like as the distinction between different materials and the possible defects of materials. These methods cannot be related to the installation defects (especially at joinings) and to the physical-mechanical service loads (temperature and relative humidity differences, moisture, dilations and contractions) of vapor barriers.
That is the reason the conventional methods provide values that permit only the selection and the quality control of vapor barriers materials.
The present invention eliminates the disadvantages of the conventional methods mentioned above because it permits the vapor barrier resistance (permeance) measurement under service conditions of temperature and moisture: "nonequilibrium" (difference) between interior and exterior air temperatures and relative humidities, installation and use conditions. The testing values are in this case real data, which can be used directly in building envelope design.
This invention permits use of the controlled atmosphere chambers supplied by heating, refrigerating and air-conditioning devices, existent in majority of the research and testing institutes.